How do you know a cotton shirt really is cotton? - Page 3

You only need to burn the end of a single thread. It's quite obvious if it's synthetic, you'll think "oh, that looks like plastic melting". It's harder to tell the differences between polyester & rayon, and cotton & wool. But usually you're worried about a synthetic fabric being used to fake a specific natural fabric.

I'm allergic to polyester, you guys can all just send your shirts to me and I will tell you if they are all cotton or not. Just be warned it may take a few months and a large number of wears for me to get a reaction.

I take a bite off the shirt cuff. You can usually tell from the taste of the shirt and after effects of consuming it. Polyester tends to have a bitter aftertaste and will give you indigestion. Cotton, being natural, acts like fiber.

The only sure way to tell what anything is made of is with a mass spectrometer.Originally they were prohibitively expensive,in the millions of dollars,but they've gotten to the point where they are affordable.Many older but functional units are available for sale to the general public:
Plasma quad 2 for only 6k:http://www.medwow.com/used-mass-spec...543260304.item
Labx has tons of them: http://www.labx.com/v2/newad.cfm?catid=12
This one is a portable self contained system,not sure of the price:http://www.kore.co.uk/ms-200.htm
This one in very compact and the base unit is only $600!: http://www.labx.com/v2/adsearch/deta...?adnumb=431314
These are amazingly tiny:http://www.labx.com/v2/adsearch/deta...?adnumb=431633
The cheapest way is to pay someplace that has one to analyze a sample,I've seen places that will test a sample for as low as $10.Most universities and decent medical labs have one,if you know someone who works there they could hook you up.I had a girlfriend who worked at WHOI who would test anything I wanted but she quit because her boss,Robert Ballard,was a douchebag(to work for).Of course it can analyze anything,not just fabric,and the possibilities are endless.